News Column

Patent Issued for Hydrogen Storage Method and System

July 8, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- From Alexandria, Virginia, NewsRx journalists report that a patent by the inventor Drnevich, Raymond Francis (Clarence Center, NY), filed on January 28, 2013, was published online on June 24, 2014 (see also Praxair Technology, Inc.).

The patent's assignee for patent number 8757926 is Praxair Technology, Inc. (Danbury, CT).

News editors obtained the following quote from the background information supplied by the inventors: "Hydrogen is utilized in a variety of industrial processes and is typically produced from the steam methane reforming of hydrocarbons that are contained in natural gas. The hydrogen after production can be used on site where the steam methane reformer is located or can be distributed to customers with the use of a pipeline.

"Customer demand will typically vary and it has been found to be advantageous to store the hydrogen when customer demand is low for later use during peak demand periods. One central advantage in storing the hydrogen is that the hydrogen production facility does not have to be sized to meet peak customer demands and thus, can be a smaller, lower cost installation. Additionally, the storage of hydrogen also allows for further profitability in that spot sales of hydrogen can be made to customers, above that required to meet contractual customer demands. Since the storage requirements related to pipeline distribution systems can be at a level of over a billion standard cubic feet of hydrogen, large underground geological formations known as salt caverns are used for such purposes.

"Salt caverns are formed by solution mining within large underground formations of salt that can be several hundred to several thousands of feet deep that are generally covered by a cap rock. In order to form the salt cavern, a well is drilled from the surface down to and through the salt formation. The well hole is supported by pipe casings which are surrounded by concrete and a smaller pipe, known as a brine string, is inserted into the casing to introduce water down into the hole. The water dissolves the salt to form the cavern and the resulting brine is pumped to the surface between the annular space formed between the casing and the smaller pipe. Additionally, brine is removed from the cavern by injecting hydrogen to pressurize the cavern and force the brine out through the brine string. When complete, the salt cavern has a roof region at the top of the salt cavern and beneath the cap rock, side regions connecting the roof regions with the bottom of the salt cavern and a residual brine layer or brine sump remaining at the bottom of the salt cavern.

"The hydrogen to be stored can be produced at the site of the salt cavern or can be removed from the pipeline itself. The hydrogen is compressed by a compressor and the resulting compressed hydrogen feed stream is introduced into the salt cavern through the casing. When the hydrogen required to meet customer demand is greater than that able to be produced by the hydrogen production facility, the hydrogen is taken from the salt cavern as a stored hydrogen stream through the casings and injected back into the pipeline.

"Carbon dioxide as well as other impurities can be introduced into the stored hydrogen stream from the salt cavern itself. The carbon dioxide impurity, as well as moisture, for the most part, evolves from the residual brine layer. Since the pipeline itself will have a specification for the amount of carbon dioxide and also, possibly moisture, that can be contained in the hydrogen that is reintroduced into the pipeline, the carbon dioxide impurity that is introduced into the stored hydrogen stream is removed by an adsorption unit that contains an adsorbent to adsorb the carbon dioxide and also possibly the moisture. For example, in U.S. Pat. No. 7,078,011, a purification system is used in connection with the salt cavern to reduce levels of carbon dioxide and moisture to sufficiently low levels that are necessary to meet the pipeline specification. It has been found that the use of carbon dioxide purification system adds a level of complexity and expense to the operation of an installation that involves the storage of hydrogen within a salt cavern. As will be discussed, it has been found that although unacceptably high levels of carbon dioxide can initially be imparted from the salt cavern to the stored hydrogen stream to be injected back into the pipeline, when the salt cavern is operated in a manner as described in the present invention, carbon dioxide removal will not be necessary."

As a supplement to the background information on this patent, NewsRx correspondents also obtained the inventor's summary information for this patent: "The present invention provides, in one aspect, a method of storing and supplying hydrogen to a hydrogen pipeline. In accordance with the method, a feed stream of the hydrogen is compressed to produce a compressed hydrogen feed stream. The compressed hydrogen feed stream is injected into a salt cavern, through at least one conduit, to produce stored hydrogen within the salt cavern and a stored hydrogen stream, composed of the stored hydrogen, is withdrawn from the salt cavern through the at least one conduit. The salt cavern has a residual brine layer located at a bottom region of the salt cavern and side regions extending upwardly from the bottom region of the salt cavern and the at least one conduit has at least one lower end located in an interior region of the salt cavern and spaced above the brine layer and from the side regions of the salt cavern. The stored hydrogen stream is introduced into the hydrogen pipeline, after having been withdrawn from the salt cavern, without removing carbon dioxide present within the stored hydrogen stream.

"The compressed hydrogen feed stream is injected into the salt cavern and the stored hydrogen stream is withdrawn from the salt cavern through at least one conduit having at least one lower end located in an interior region of the salt cavern and spaced above the brine layer and from the side regions of the salt cavern. At least a minimum quantity of the stored hydrogen is maintained within the salt cavern before, during, and between times at which the compressed hydrogen feed stream is injected and at which the stored hydrogen stream is withdrawn such that a stagnant layer of hydrogen is maintained that borders the interior region and has at least a bottom portion overlying the residual brine layer and a lateral portion situated along the side regions of the salt cavern. The stagnant layer has a carbon dioxide content that is a potential source of carbon dioxide contamination to the stored hydrogen stream. The flow rates and the velocities at which the compressed hydrogen feed stream is injected into the salt cavern and the stored hydrogen stream is withdrawn the salt cavern are limited such that the stagnant layer is not disturbed and the carbon dioxide contamination of the stored hydrogen stream from the stagnant layer is inhibited.

"As a result, for the most part, any carbon dioxide contained in the stored hydrogen stream is a result of the carbon dioxide contained in the salt cavern. However, any such carbon dioxide contamination is at an extremely low level given that it will arise from molecular diffusion of the hydrogen from the stagnant layer to the interior region and such transport of hydrogen is an extremely slow process. As such, carbon dioxide removal is not necessary.

"The at least one lower end of the at least one conduit can be spaced below a top region of the salt cavern, located opposite to the bottom region of the salt cavern. In such case, the stagnant layer also has a top portion extending along the top region of the salt cavern and situated opposite to the bottom portion of the stagnant layer. Water can be removed from the stored hydrogen stream prior to injection into the pipeline. Further, the hydrogen feed stream can be compressed to a pressure above the pipeline pressure within the pipeline and as a result, the stored hydrogen has a cavern pressure that is above the pipeline pressure. The stored hydrogen stream can therefore be removed from the salt cavern as a consequence of the cavern pressure and the stored hydrogen stream is reduced to the pipeline pressure prior to injecting the stored hydrogen stream into the pipeline.

"In another aspect of the present invention, a system is provided for storing and supplying hydrogen to a hydrogen pipeline. A compressor is provided for compressing a feed stream of the hydrogen to produce a compressed hydrogen feed stream. A salt cavern is incorporated into the system and has a residual brine layer located at a bottom region of the salt cavern and side regions extending upwardly from the bottom region of the salt cavern. At least one conduit is in communication with the salt cavern for injecting the compressed hydrogen feed stream into a salt cavern to produce stored hydrogen within the salt cavern and for withdrawing a stored hydrogen stream composed of stored hydrogen from the salt cavern. The at least one conduit has at least one lower end located in an interior region of the salt cavern and spaced above the brine layer and from the side regions of the salt cavern. A flow network is configured to selectively connect the compressor to the at least one conduit such that the compressed hydrogen feed stream is injected into the salt cavern to produce the stored hydrogen within the salt cavern and to selectively connect the at least one conduit to the hydrogen pipeline such that the stored hydrogen stream is injected into the pipeline without removing carbon dioxide contained in the stored hydrogen stream.

"The salt cavern has at least a minimum quantity of the stored hydrogen within the salt cavern before, during, and between times at which the compressed hydrogen feed stream is injected and at which the stored hydrogen stream is withdrawn such that a stagnant layer of hydrogen is maintained that has at least a bottom portion overlying the residual brine layer and a lateral portion situated along side regions of the salt cavern. The stagnant layer has a carbon dioxide content that is a potential source of carbon dioxide contamination to the stored hydrogen stream. A means is provided for limiting the flow rates and the velocities at which the compressed hydrogen feed stream is injected into the salt cavern and the stored hydrogen stream is withdrawn from the salt cavern such that the stagnant layer is not disturbed and the carbon dioxide contamination of the stored hydrogen stream from the stagnant layer is inhibited.

"The at least one lower end of the at least one conduit can be spaced below a top region of the salt cavern, located opposite to the bottom region of the salt cavern. In such case, the stagnant layer also has a top portion extending along the top region of the salt cavern and situated opposite to the bottom portion of the stagnant layer. The flow network can be provided with a drying unit positioned within the flow network to remove water from the stored hydrogen stream prior to injection into the pipeline. The compressor compresses the hydrogen feed stream such that the compressed hydrogen feed stream is injected into the salt cavern at a cavern pressure that is above the pipeline pressure. The flow network is configured to reduce the pressure of the stored hydrogen stream to the pipeline pressure prior to injecting the stored hydrogen stream into the pipeline.

"In either aspect of the present invention, the at least one conduit can have an injection conduit and a withdrawal conduit. The compressed hydrogen feed stream is injected into the salt cavern through the injection conduit and the stored hydrogen stream is withdrawn from the salt cavern through the withdrawal conduit. The at least one conduit can also comprise an injection conduit having a flow diffuser from which at least the compressed hydrogen feed stream is injected into the salt cavern.

"Furthermore, in either aspect of the present invention, the minimum volume of the hydrogen stored within the salt cavern can be maintained at a volume ratio equal to a stored volume of the hydrogen to the actual cavern volume of no less than 29.0 scf/cf. It is to be noted here that, as used herein and in the claims, the unit 'scf/cf' means standard cubic feet of the stored hydrogen per actual cubic feet of the cavern volume able to contain the stored hydrogen. The actual cubic feet of cavern volume able to contain the stored hydrogen is computed by subtracting the volume of the residual brine layer from the total volume of the salt cavern. In case the at least one lower end of the at least one conduit is open, rather than incorporating a flow diffuser, the at least one lower end of the at least one conduit can be spaced from the residual brine layer at a lower vertical distance of no less than 250 feet and is also spaced from the side regions of the salt cavern at a lateral distance of no less than 40 feet as measured from a vertical line extending between 10 and 250 feet below the at least one lower end of the at least one conduit. The flow rates and velocities are limited such that, as measured at the at least one lower end of the at least one conduit, the compressed hydrogen feed stream is injected at an injection ratio equal to an injection flow rate of the compressed hydrogen feed stream to the actual cavern volume of no greater than 7.5 scfd/cf and at an injection velocity of the compressed hydrogen feed stream of no greater than 100 feet per second and the stored hydrogen stream is withdrawn at a withdrawal ratio equal to the withdrawal flow rate of the stored hydrogen stream to the actual cavern volume of no greater than 10.0 scfd/cf and at a withdrawal velocity of the stored hydrogen stream of no greater than 150 feet per second. It is to be mentioned that, as used herein and in the claims, the unit 'scfd/cf' means the flow rate measured in standard cubic feet per day per cubic feet of the actual cavern volume that is able to store the stored hydrogen.

"Where the at least one lower end of the at least one conduit is spaced below a top region of the salt cavern, the at least one lower end can be spaced from the top region of the salt cavern at an upper vertical distance of no less than 50 feet.

"In the aspect of the present invention relating to the method, where the hydrogen feed stream contains less than 1.0 ppmv carbon dioxide and less than 8 ppmv carbon monoxide, a sum of a carbon dioxide content and carbon monoxide content in the stored hydrogen stream is to be less than 10 ppmv. Where hydrogen feed stream contains less than 0.1 ppmv carbon dioxide and less than 0.6 ppmv carbon monoxide, a sum of a carbon dioxide content and carbon monoxide content in the stored hydrogen stream is less than 1.0 ppmv. The unit 'ppmv' as used herein and in the claims means parts per million by volume on a dry basis or in other words without considering the water content."

For additional information on this patent, see: Drnevich, Raymond Francis. Hydrogen Storage Method and System. U.S. Patent Number 8757926, filed January 28, 2013, and published online on June 24, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8757926.PN.&OS=PN/8757926RS=PN/8757926

Keywords for this news article include: Gases, Elements, Hydrogen, Chemistry, Carbon Dioxide, Carbon Monoxide, Inorganic Chemicals, Praxair Technology Inc., Inorganic Carbon Compounds.

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Source: Life Science Weekly


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